Primary 1 Mathematics Length Quiz

Primary 1 Mathematics Quiz - Length (Answer Key)

Total Marks: 20

Section A: Multiple Choice Questions (Questions 1–8, 8 marks)

1. Answer: B (centimetre / cm)
Marks: 1
Explanation: A pencil is a small object, typically 10–20 cm long. Centimetre (cm) is the appropriate unit for measuring small objects like pencils, books, and toys. Metre (m) is for longer lengths (e.g., height of a door), kilometre (km) is for very long distances (e.g., between towns), and millimetre (mm) is for very tiny lengths (e.g., thickness of a coin).
Common mistake: Choosing metre (m) because it is a familiar unit.

2. Answer: A (8 cm)
Marks: 1
Explanation: The crayon starts at the 2 cm mark and ends at the 10 cm mark. To find the length, subtract the starting mark from the ending mark: 10 cm – 2 cm = 8 cm.
Key concept: When an object does not start at 0 cm, length = end reading – start reading.
Common mistake: Reading the end mark (10 cm) directly as the length.

3. Answer: B (A pencil (15 cm))
Marks: 1
Explanation: Compare the given lengths: paper clip = 3 cm, pencil = 15 cm, eraser = 4 cm, sharpener = 2 cm. The greatest number is 15 cm, so the pencil is the longest.
Key concept: To find the longest, compare the numerical values of the lengths.

4. Answer: A (8 cm)
Marks: 1
Explanation: "How much longer" means find the difference. Length of book = 20 cm, length of notebook = 12 cm. Difference = 20 cm – 12 cm = 8 cm.
Key concept: Difference = longer length – shorter length.

5. Answer: A (18 cm)
Marks: 1
Explanation: Original string = 30 cm. Cut off = 12 cm. Remaining = 30 cm – 12 cm = 18 cm.
Key concept: Remaining length = original length – length cut off.

6. Answer: A (Diagram A)
Marks: 1
Explanation: The correct way to measure length with a ruler:

• Place the ruler straight alongside the object.
• Align the start of the object with the 0 cm mark (not 1 cm or 2 cm).
• Ensure no gap between the object and the ruler.
• Read the marking at the end of the object.
  Diagram A shows all these correct steps. Diagram B starts at 2 cm (would need subtraction). Diagram C has the ruler placed diagonally (inaccurate). Diagram D has a gap at the start (inaccurate).

7. Answer: A (3 cm, 5 cm, 9 cm, 12 cm)
Marks: 1
Explanation: Arrange from smallest (shortest) to largest (longest): 3 < 5 < 9 < 12. So the order is 3 cm, 5 cm, 9 cm, 12 cm.

8. Answer: C (65 cm)
Marks: 1
Explanation: "Total length" means add the two lengths together. Ribbon = 25 cm, Rope = 40 cm. Total = 25 cm + 40 cm = 65 cm.

Section B: Short Answer Questions (Questions 9–16, 8 marks)

9. Answer: m (metre)
Marks: 1
Explanation: A standard door height is about 2 metres (200 cm). Using centimetres would give 200 cm, which is an unnecessarily large number for everyday description. The unit "metre" is used for longer lengths like height of a room, length of a bed, or width of a classroom.

10. Answer: cm (centimetre)
Marks: 1
Explanation: A paper clip is a very small object, about 3 cm long. Using metres would give 0.03 m, which is not practical for describing such a tiny length. Centimetre is the standard unit for small objects like stationery, toys, and hand spans.

11. Answer: 14 cm
Marks: 1
Explanation: The paintbrush starts at the 0 cm mark and ends at the 14 cm mark. Since it starts at 0, the length is simply the end reading: 14 cm.
Key concept: When an object starts at 0 cm, length = end reading.

12. Answer: 4 cm
Marks: 1
Working: 14 cm – 10 cm = 4 cm
Explanation: The pen is 14 cm, the pencil is 10 cm. To find how much longer, subtract: 14 – 10 = 4 cm.

13. Answer: 25 cm
Marks: 1
Working: 18 cm + 7 cm = 25 cm
Explanation: "Total length" means addition. First piece = 18 cm, second piece = 7 cm. Total = 18 + 7 = 25 cm.

14. Answer: 18 cm
Marks: 1
Working: 6 paper clips × 3 cm each = 18 cm
Explanation: There are 6 paper clips placed end-to-end. Each is 3 cm. Total length = 3 + 3 + 3 + 3 + 3 + 3 = 18 cm (or 6 × 3 = 18 cm). This introduces the idea of repeated addition / multiplication for equal groups.

15. Answer: 35 cm
Marks: 1
Working: 50 cm – 15 cm = 35 cm
Explanation: Original ribbon = 50 cm. Used = 15 cm. Left = 50 – 15 = 35 cm.

16. Answer: 50 cm
Marks: 1
Working: 100 cm – 50 cm = 50 cm
Explanation: Table = 100 cm, Chair = 50 cm. Difference = 100 – 50 = 50 cm. The table is 50 cm longer than the chair.

Section C: Word Problems (Questions 17–20, 4 marks)

17. Answer: 35 cm
Marks: 1
Working:
Total length of cloth = 60 cm
Length of first piece = 25 cm
Length of second piece = 60 cm – 25 cm = 35 cm
Explanation: When a whole is cut into two parts, the whole = part 1 + part 2. To find the missing part, subtract the known part from the whole: 60 – 25 = 35 cm.
Marking note: 1 mark for correct answer with or without working shown. Accept "35 cm" or "35".

18. Answer: 47 cm
Marks: 1
Working:
Length of red rope = 35 cm
Blue rope is 12 cm longer = 35 cm + 12 cm = 47 cm
Explanation: "12 cm longer than" means add 12 cm to the given length. 35 + 12 = 47 cm.
Common mistake: Subtracting instead of adding (35 – 12 = 23).
Marking note: 1 mark for correct answer with or without working shown.

19. Answer: 15 cm
Marks: 1
Working:
Total length of stick = 40 cm
First piece = 15 cm
Second piece = 10 cm
Length of first two pieces = 15 cm + 10 cm = 25 cm
Third piece = 40 cm – 25 cm = 15 cm
Explanation: The stick is broken into 3 pieces. Total = sum of all 3 pieces. Add the two known pieces (15 + 10 = 25), then subtract from the total (40 – 25 = 15).
Marking note: 1 mark for correct answer. Award mark if working shows 40 – 15 – 10 = 15 or 40 – (15 + 10) = 15.

20. Answer: 8 m
Marks: 1
Working:
Length of ruler = 1 m
Number of times placed = 8
Length of classroom = 8 × 1 m = 8 m
Explanation: Each placement of the 1-metre ruler covers 1 metre. Placing it 8 times end-to-end gives 8 metres. This connects repeated addition (1+1+1+1+1+1+1+1) to multiplication (8 × 1).
Marking note: 1 mark for correct answer. Accept "8 m" or "8 metres".

End of Answer Key